Four suspected al Qaeda militants targeted in a government military operation this week have been found in a Yemeni hospital, the Interior Ministry said on Saturday, Reuters reported.
In south Yemen, supporters of a separatist movement demonstrated in protest against civilian deaths in the raids.
The government website "September 26" said Saudi nationals were among al Qaeda suspects killed in the operation.
Yemen said on Thursday its security forces and warplanes foiled a planned series of suicide bombings by attacking targets including an al Qaeda training center in the southern province of Abyan and sites in Arhab district.
About 30 al Qaeda militants were killed and 17 arrested in Abyan and in Arhab, northeast of the capital Sanaa, it said.
Hundreds of people from the opposition Southern Movement, which says south Yemen has been marginalized and wants it to secede, protested in Radfan, Zinjibar and Dalea on Saturday against civilian deaths in the raids.
The four Yemenis were found in a hospital in Aden and placed under arrest, the ministry said. Their families had taken them there after the attack in Abyan.
The New York Times reported on Saturday that the United States gave military hardware, intelligence and other support to Yemeni forces to carry out the raids.
Saudi and Yemeni militants said earlier this year they were uniting under the name Al Qaeda in the Arabian Peninsula, using Yemen as their base.
Saudi Arabia, the world's biggest oil exporter, fears instability in Yemen could turn into a security threat for the kingdom by allowing al Qaeda to gain a stronger foothold in its fragile neighbor.
Yemen's opposition accused the government on Friday of killing dozens of civilians, including whole families, in the raids on Thursday.
U.S. President Barack Obama called Yemeni President Ali Abdullah Saleh, saying the operation "confirms Yemen's resolve in confronting the danger of terrorism represented by al Qaeda for Yemen and the world," Yemen's state media said.
Besides fighting al Qaeda militants and separatist unrest, the Arab world's poorest country is fighting a war against Shi'ite rebels in the north.
Political analysts say such conflicts, together with falling oil income, water shortages and a humanitarian crisis, add to instability in a region that includes oil superpower Saudi Arabia and one of the world's busiest shipping lanes.